Re: [PATCH hotfix 6.12 v4 4/5] mm: refactor arch_calc_vm_flag_bits() and arm64 MTE handling

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Wed, Oct 30, 2024 at 12:09:43PM +0100, Vlastimil Babka wrote:
> On 10/30/24 11:58, Catalin Marinas wrote:
> > On Wed, Oct 30, 2024 at 10:18:27AM +0100, Vlastimil Babka wrote:
> >> On 10/29/24 19:11, Lorenzo Stoakes wrote:
> >> > --- a/arch/arm64/include/asm/mman.h
> >> > +++ b/arch/arm64/include/asm/mman.h
> >> > @@ -6,6 +6,8 @@
> >> >
> >> >  #ifndef BUILD_VDSO
> >> >  #include <linux/compiler.h>
> >> > +#include <linux/fs.h>
> >> > +#include <linux/shmem_fs.h>
> >> >  #include <linux/types.h>
> >> >
> >> >  static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
> >> > @@ -31,19 +33,21 @@ static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
> >> >  }
> >> >  #define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
> >> >
> >> > -static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
> >> > +static inline unsigned long arch_calc_vm_flag_bits(struct file *file,
> >> > +						   unsigned long flags)
> >> >  {
> >> >  	/*
> >> >  	 * Only allow MTE on anonymous mappings as these are guaranteed to be
> >> >  	 * backed by tags-capable memory. The vm_flags may be overridden by a
> >> >  	 * filesystem supporting MTE (RAM-based).
> >>
> >> We should also eventually remove the last sentence or even replace it with
> >> its negation, or somebody might try reintroducing the pattern that won't
> >> work anymore (wasn't there such a hugetlbfs thing in -next?).
> >
> > I agree, we should update this comment as well though as a fix this
> > patch is fine for now.
> >
> > There is indeed a hugetlbfs change in -next adding VM_MTE_ALLOWED. It
> > should still work after the above change but we'd need to move it over
>
> I guess it will work after the above change, but not after 5/5?
>
> > here (and fix the comment at the same time). We'll probably do it around
> > -rc1 or maybe earlier once this fix hits mainline.
>
> I assume this will hopefully go to rc7.

To be clear - this is a CRITICAL fix that MUST land for 6.12. I'd be inclined to
try to get it to an earlier rc-.

>
> > I don't think we have
> > an equivalent of shmem_file() for hugetlbfs, we'll need to figure
> > something out.
>
> I've found is_file_hugepages(), could work? And while adding the hugetlbfs
> change here, the comment could be adjusted too, right?

Right but the MAP_HUGETLB should work to? Can we save such changes that
alter any kind of existing behaviour to later series?

As this is going to be backported (by me...!) and I don't want to risk
inadvertant changes.

>
> >
> >> >  	 */
> >> > -	if (system_supports_mte() && (flags & MAP_ANONYMOUS))
> >> > +	if (system_supports_mte() &&
> >> > +	    ((flags & MAP_ANONYMOUS) || shmem_file(file)))
> >> >  		return VM_MTE_ALLOWED;
> >> >
> >> >  	return 0;
> >> >  }
> >
> > This will conflict with the arm64 for-next/core tree as it's adding
> > a MAP_HUGETLB check. Trivial resolution though, Stephen will handle it.

Thanks!

> >
>